A surfactant is generally used for washing metal members or the like, as a wash fluid mixed with, for example, a chelating agent, an alkaline agent and the like, in water. In this case, the surfactant removes oil smudge adhered to a surface of a metal member, by aggregating around the smudge to form a micelle that encloses the smudge, and diffusing through the fluid. The chelating agent enhances a washing effect by dissolving an oxide film present at an interface between a clean surface of the metal member and the smudge, into the wash fluid. The alkaline agent enhances detergency by interacting with the surfactant, and improves wettability, permeability and the like of the smudge to the wash fluid, by solubilizing the smudge through a reaction in the wash fluid to disperse the smudge, as well as by reducing a critical micelle concentration and surface tension of the surfactant.
In general, the surfactant is classified into anionic surfactant, cationic surfactant, nonionic surfactant, and ampholytic surfactant. Among these, the anionic surfactant and the ampholytic surfactant exhibit detergency, and used as a main component of the wash fluid. On the other hand, the cationic surfactant has a higher affinity with oil, and accordingly, in washing metal members or the like, the cationic surfactant is used together with a wash fluid containing the anionic surfactant, the ampholytic surfactant or the like, in order to prevent oil from being solubilized and emulsified in the wash fluid, and in the case of the wash fluid in an emulsified state, to decompose emulsified matters, so that the detergency of the wash fluid lasts for a long time period. For such a cationic surfactant, a quaternary ammonium salt has been known (see, for example, Patent documents 1 and 2).    Patent document 1: JP6-293896A    Patent document 2: JP2005-187622A